1. Field of The Invention
The present invention relates generally to system for monitoring and controlling low concentrations of reactive gasses and, more particularly, to a system for monitoring and controlling concentrations of ethylene gas.
2. Related Art
Perishable produce such as fruit, vegetables and cut flowers, must be consumed while fresh. To facilitate this, an elaborate distribution system has been developed to deploy rapidly harvested produce into supermarkets, restaurants, and other food stores. Produce that is not timely consumed must be destroyed or otherwise discarded. Optimal flow of produce through this distribution chain is important to minimize the amount of produce that must be discarded.
It is well known that the rate at which the produce ages may be controlled by controlling the concentration of ethylene in the atmosphere surrounding the produce. This is related to the fact that ethylene is a plant growth hormone. For many products, exposure to ethylene, even in low concentrations, speeds the aging process. If ethylene concentration levels are not controlled and rise above unacceptable levels, premature ripening or decay of the produce can occur, which may require the produce to be discarded before it is able to be sold.
It has been found that reducing the concentration of ethylene is important during transportation and storage of produce that naturally emits ethylene gas. For example, ventillating to remove excess ethylene has been found to reduce the rate of decay for many fruits and vegetables and is also particularly useful for maintaining the robustness of cut flowers, such as tulips, imported into the United States from Holland.
It is sometimes financially advantageous to pick oranges while still green and cause the peel to change color subsequent to harvesting. As is well known, exposing a green colored orange to a low concentration of ethylene gas over a long period of time (24-72 hours) causes the chlorophyll in the orange peel to break down, thus causing the orange peel to change color. This process will be referred to herein as "degreening."
Ethylene concentration between about 5 to 10 parts per million (ppm) affect the chlorophyll in the peel without penetrating into the fruit itself. Higher concentrations of ethylene, above about 10-15 ppm, however, have been found to cause the peel to break down and may cause the onset of mold in the peel. When this happens, the entire batch of fruit frequently must be discarded. By contrast, an insufficient amount of ethylene, below about 5 ppm, will delay the degreening process, thus inhibiting distribution of the current batch of fruit as well as batches of fruit waiting to enter the degreening rooms. Accordingly, controlling the concentration of ethylene during the degreening process is critical.
Controlling the concentration of ethylene has yet another use. Since ethylene is a plant growth hormone, increasing the concentration of ethylene may speed the ripening process for certain types of products. For example, it has been found that exposing tomatoes and bananas to ethylene in a concentration of about 100 ppm for a period of 12-24 hours will speed the ripening process for these products. Typically, a stepped process is used whereby the concentration is varied over time. Likewise, it is thus envisioned that controlled levels of ethylene gas could be used to stimulate plant production in outer space, should this ever become a reality.
Thus, monitoring and controlling the concentration of ethylene is important in many situations, especially during the production, transportation and storage of produce, during degreening of oranges, while ripening tomatoes and bananas and, potentially, in connection with growing plants in a controlled environment such as outer space. Unfortunately, detecting accurately ethylene concentrations, especially at the very low levels associated with degreening, is not trivial. Accordingly, there is a need for a system that can accurately monitor and control low concentrations of ethylene gas.